[time-nuts] Issues with Datum FTS 4065A cesium beam reference

[Magnus Danielson]

Hi Jim,

On 2020-07-27 03:48, AC0XU (Jim) wrote:
> Time Nuts-
>
> Having fixed the dead power supply on this Datum FTS 4065A, the control panel displays mostly "Major" fault, although this occasionally shifts to "Minor" fault for a brief time. It reports Cesium Module faults that vary from time to time. They are usually one of:
>
> 2,18
> 2,3,18
> 2,3,7,18
>
> According to the 4065C manual, the codes mean:
>
> 2 - Voltage difference (symmetry check of clock transition) > 40 mV
> or
> Voltage difference (clock pedestal) >40 mV
>
> 3 - Voltage difference (Zeeman pedestal) >160 mV
>
> 7 -  DAC voltage < 5% or > 95% of input range
>
> 18 - Beam Gain DAC Near Limit
These is in increasing order of severity.
> Is there a straightfoward way to determine whether the tube is dead or - how should I drill down??
>
> All voltages displayed by the control panel seem to be within range. Oscillator shifts from 'COLD' to 'warm'. There is a 10 MHZX output signal but it is not especially stable.

One of the things to care about after having a major power-fault is that
the oscillator may need time to recover. Locking it up while it is
drifting and being too far of frequency upset any cesium. Measure the 10
MHz and let it settle. Only after it has settled one may consider tuning
it. If it is close enough it may lock up, and that goes quicker with a
more accurate 10 MHz straight from the OCXO.

Locking onto the Zeeman and then clock transition becomes easier.

Cesium locks goes quick by H-maser standards.

Cheers,
Magnus